1. Field of the Invention
The present invention relates to a continuous paper duplex printer and a printing method. The present invention also relates to single sided printing performed by the continuous paper duplex printer for printing an image (front image) on a page at the front of continuous paper in parallel with the printing of an image (back image) on a page that is different from the page mentioned above and is at the back of the continuous paper.
2. Description of the Related Art
Already known is an image forming system in which a printer controller once receives a printing request from a host apparatus (computer), and then, a printer (image forming apparatus) connected to the printer controller via an interface (I/F) performs printing. Moreover, already known as a printer that employs continuous paper and that enables high-speed printing is a printer that can linearly change a paper feed speed in order to prevent damage to paper from abrupt stop of paper feed. The printer includes therein an I/F and an I/F controller for responding to a printer controller, a printing mechanism, an image processing apparatus that corrects image data transmitted from the printer controller so as to match the image forming characteristics of the printing mechanism, and a process controller that controls the printing mechanism.
Japanese Patent Application Laid-open No. H8-2017 (see FIG. 5 of the publication) discloses an example of a continuous paper printer (hereinafter, referred to as a Single Engine Duplex (SED) system continuous paper printer) that enables duplex printing to be parallelly performed. In the example, for enabling duplex printing by a single continuous paper printer, the front surface of paper having a width that is a half size of the physical width of an image transfer unit provided at a printing mechanism is printed using a half side of the image transfer unit. Subsequently, the paper is reversely fed via a paper feed path and then is printed using the other half side of the image transfer unit again. Japanese Patent Application Laid-open No. H8-2017 also discloses a continuous paper printer (see FIG. 10 of the publication) in which two printing mechanisms are arranged in a tandem (serial) manner. In the continuous paper printer, the first printing mechanism forms an image on the front surface of continuous paper, and after the continuous paper is reversed, the second printing mechanism forms an image on the back surface of the paper as well. Thus, the second printing mechanism performs the image formation on the back surface in parallel with the image formation on the front surface performed by the first printing mechanism. Both of the printers have time difference between the formation of a front surface image and the formation of a back surface image for forming an image on the back of the front surface image. In other words, an image (front image) is printed on a page at the front of continuous paper while a back image that needs to be formed on the back surface of a page different from the page mentioned above is formed at the back of the continuous paper in parallel. Accordingly, time difference occurs between image formation of one of the page frames on the front surface of the continuous paper that corresponds to a sheet of cut paper and the image formation on the back surface of the front surface.
FIG. 6 is a schematic of an SED system continuous paper printer. Continuous paper 1 passes through an area that is at the left half of a recording drum 3 of an image forming mechanism 2 whose image forming area is two or more times larger than the width of the continuous paper 1 and that is at the left half of a roller 4. For duplex printing, the image forming mechanism 2 forms an image on the front surface of the continuous paper 1. Subsequently, the continuous paper 1 passes around a reverse roller 5 and return rollers 6 and 7 and then passes through an area that is at the right half of the recording drum 3 of the image forming mechanism 2 and that is at the right half of the roller 4 in a reversed state. The image forming mechanism 2 forms an image on the back surface of the continuous paper 1 that is reversed to serve as the front surface.
An image data processing system in the conventional SED system continuous paper printer starting from the printer controller includes three of a front surface image processing apparatus, a back surface image processing apparatus, and an image process controller. The front surface image processing apparatus and the back surface image processing apparatus perform image processing for pages to be printed. The image process controller (an I/F controller and a process controller) notifies the state of the printer and performs synchronization control of, front surface image processing and back surface image processing.
FIG. 7 is a timing chart for illustrating data transmission from a printer controller 21 to a front surface image processing apparatus 27 and a back surface image processing apparatus 28 in the conventional SED system continuous paper duplex printer during single sided print job processing. For the conventional single sided printing, the printer controller 21 transmits print image data (image data) produced according to the print job to the front surface image processing apparatus 27 and transmits a blank page instruction for the back surface of a sheet to the back surface image processing apparatus 28. Every time the transmission of the image data or the blank page instruction to the front surface image processing apparatus 27 or to the back surface image processing apparatus 28 is completed, a completion notice of page data transmission is provided to an image process controller (an I/F controller 25 and a process controller). The front surface image processing apparatus 27 performs image processing on the received image data and then provides a notice of a page data printable state to the process controller (not illustrated). In contrast, the back surface image processing apparatus 28 receives the blank page instruction from the printer controller 21, thus does not need to perform image processing, and therefore, provides the notice of a page data printable state to the process controller, upon receipt of the instruction. The process controller waits until the notices of a page data printable state are received from both the front surface image processing apparatus 27 and the back surface image processing apparatus 28. Subsequently, the process controller provides a paper feed instruction to a printing mechanism and also instructs the front surface image processing apparatus 27 and the back surface image processing apparatus 28 to transmit the image data to the printing mechanism.
In such a manner, during the printing of the single sided print job that is performed by the conventional SED continuous paper printer, the printer controller 21 makes only the front surface image processing apparatus 27 perform image processing of a printing image and transmits a blank page command to the back surface image processing apparatus 28. Therefore, during the printing of the single sided print job, processing is focused on the front surface image processing apparatus 27, and the back surface image processing apparatus 28 performs no processing. Thus, resources cannot be efficiently utilized.
Japanese Patent No. 3852148 discloses a method of controlling duplex printing for continuous paper that enables efficient printing even when a drum for a front surface is distanced from a drum for a back surface. In the method, in order to make a continuous paper printer efficiently perform duplex printing, a control device includes therein a front surface queue and a back surface queue (memories) per page, and when no image is printed on the back surface of paper, no operation (NOP) data is put in the queue. However, this method cannot improve productivity during single sided printing.
Japanese Patent Application Laid-open No. 2009-58623 discloses a system in which when two printers perform printing on cut paper, the first printer prints odd-numbered pages, and the second printer prints even-numbered pages in order to equalize toner consumption. However, even the technique of Japanese Patent Application Laid-open No. 2009-58623 cannot improve productivity during single sided printing.